San Francisco-based Yammer said Wednesday that it has acquired OneDrum, a UK-based firm developing file sharing and collaboration software for the business market. Financial terms of the buy were not disclosed. Yammer said that all of OneDrum's employees will be joining Yammer. OneDrum was headed by Jasper Westaway, who joins the lead up integration efforts between the two firms. OneDrum's file sharing and collaboration software allows users to share Word, Excel, PowerPoint, and other documents in real time.